Does HLA-DQA1 rs2187668 CT increase gluten-related immune susceptibility and make stool anti-gliadin IgA more relevant to thyroid autoimmunity risk?

The gut-thyroid axis represents a key interface in autoimmune pathology, particularly in individuals with specific genetic predispositions that alter mucosal and systemic immune reactivity.

Genetic susceptibility and shared mechanisms

• Shared autoimmune background: The HLA-DQA1 rs2187668 CT genotype serves as a robust tag for the HLA-DQ2.5 haplotype. This variant functions within a shared HLA-DQ2.5/DR3 genetic background, which significantly increases susceptibility to both gluten-driven immune activation and autoimmune thyroiditis.
• Humoral immune pathways: In individuals with gluten susceptibility, immune activation leads to elevated serum anti-gliadin and anti-tissue transglutaminase (tTG) antibodies. These serum antibodies are clinically established correlates and predictors of elevated thyroid autoantibodies, reflecting systemic immune cross-reactivity.

Fecal markers vs. systemic clinical evidence

• Mucosal reactivity: Stool (fecal) anti-gliadin IgA acts as a localized indicator of gut mucosal immune response to gluten. In carriers of the rs2187668 CT genotype, secretory IgA complexes facilitate the mucosal transport of gliadin, which acts as the upstream driver of systemic inflammation.
• Diagnostic limitations: Despite the biological plausibility of this gut-thyroid connection, direct evidence linking stool anti-gliadin IgA to thyroid autoimmunity risk is currently lacking. While serum anti-gliadin antibodies are validated markers of systemic risk, stool IgA is not yet clinically established as a predictive tool for thyroid autoimmunity.

Bottom line

• The HLA-DQA1 rs2187668 CT genotype firmly increases susceptibility to gluten-related immune activation through a shared HLA-DQ2.5/DR3 autoimmune background. However, while mucosal gluten reactivity is an upstream driver of systemic inflammation, utilizing stool anti-gliadin IgA to evaluate thyroid autoimmunity risk is a biologically plausible concept that currently lacks direct clinical validation.